


Random Undertale Headcanons

by StellarOwl



Category: Undertale (Video Game)
Genre: Gen, headcanons
Language: English
Status: Completed
Published: 2020-11-26
Updated: 2020-11-26
Packaged: 2021-03-10 02:01:08
Rating: General Audiences
Warnings: No Archive Warnings Apply
Chapters: 5
Words: 3,028
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/27725852
Author URL: https://archiveofourown.org/users/StellarOwl/pseuds/StellarOwl
Summary: It is what it says on the tin: Undertale headcanons that I accumulated while playing Undertale and consuming Undertale fan content.
Relationships: Papyrus & Sans (Undertale)
Kudos: 12





	1. Skeleton Brothers

**Author's Note:**

> This one's about headcanons for how things work, like magic and stuff, mostly. I plan to make a second list for the headcanons that are more about characters' opinions about certain things. You don't have to read them in order, but I'm going to list them as a series because they kind of go together. Enjoy!

  * **How the conveniently-shaped lamp trick actually worked:** From the angle he was standing, Papyrus could see Frisk hiding behind the lamp, but he didn’t know they were a human. When Sans suggested that he go check out the lamp, Papyrus reasoned that Sans must be working together with this monster child to prank him, and that as soon as he went over there, the monster child would jump out and tackle him, or shout “boo”, or something like that. So, he refused to play Sans’s game and ignored the kid.



  * At the end of True Pacifist, when Sans walks the wrong direction, he actually is going to stop Papyrus from making a mess of things. He’s just taking a shortcut. Undyne, however, doesn’t know that he can teleport and assumes that he’s leaving her to take responsibility as usual. Boy is she surprised when she chases Papyrus down the mountain and finds Sans already standing there.



  * Since Papyrus has a bedtime story but thinks sleeping 7 hours is ridiculous, he most likely gets back up to do stuff after, like, the exact minimum time needed until Sans falls asleep. I think skeletons don’t necessarily need sleep, it’s an optional thing. He really only requests a story so he can spend more time with his big bro, and it’s adorable. And Sans enjoys story time just as much as Papyrus does.



  * Some people think Mysteryman is Gaster. Some think [REDACTED] is Gaster. I think they're both right. Gaster was shattered across time and space, after all. The Memoryheads are also fragments of Gaster.



  * OK so, you know how Papyrus's room and Sans's room look like they shouldn't fit in the house based on their sizes, but if they swapped places, they would fit? My theory is Sans was messing around with dimensional stuff and got the doors swapped around. It's similar to how the jokebook-in-a-textbook-in-a-jokebook thing happened, actually. Here, have a little thing I wrote about it:



So, picture this: Sans is sitting on the couch reading, he’s got a theoretical physics book and a magic book open at the same time for “multitasking” because of course he does, and he notices something in the two books that seems similar, and he gets an idea.

He tries it out on something small first, like opening a textbook to find a joke book inside it rather than its usual contents, and when that works, he just gets this big grin on his face. For days after that Papyrus is just opening doors and cabinets in the house only to find them leading to the wrong place or holding the wrong thing.

He _knows_ Sans is behind it somehow, and he can’t seem to get Sans back for it because wherever he sets up his own traps and pranks, Sans _somehow_ conveniently gets around them (read: teleports). Eventually, Sans calms down with the door tricks, but it’s been going on so much and for so long that their bedroom doors are permanently switched around, and neither of them realizes.

  * Sans doesn’t just take naps because he’s depressed or because his low stats mean he wears out faster. It’s actually a survival strategy. Sleeping can recover your HP above the maximum. His maximum is 1 HP. If he wants to be able to take more than one hit, he needs to sleep a lot. This is why he was able to survive Flowey tying him up in thorny vines during the True Ending. Also, Sans never told Papyrus about the whole 1HP thing because he didn’t want him to worry or treat him differently, so Papyrus just thinks Sans is being lazy.



  * Sans didn’t immediately remember Gaster. He forgot, like everyone else. He figured it out the same way he found out about resets: he noticed that something was off, did some investigating/research, and managed to put the pieces together (metaphorically, I mean. Gaster is still pretty scattered).



  * Sans, like Papyrus, is able to fly thanks to his gravity powers. He just chooses not to, because why fly when you can teleport? I’m also pretty sure Papyrus doesn’t even realize he’s doing anything weird when he’s flying.



  * OK so you know how Sans has glowy eyes most of the time (only turns them off when he’s being intimidating) but Papyrus doesn’t? I think the glowy things are expressive magic, something that monsters choose to do for fun, when they’re in a good mood, to express themselves, etc. Sans uses his eyeglows to show when he’s being facetious, which is 90% of the time. Papyrus, who genuinely does get excited about things, refuses to use eyeglows, probably because he wants to look more serious and intimidating.



  * I think Sans figures out that you’re the anomaly at some point during the Hotland arc, which is why he shows up to have that talk before you enter the CORE. When he said “you’d be dead where you stand,” he didn’t mean he would have killed you back in Snowdin, he meant he would have killed you right there in the restaurant because he figured out you’re the one who’s resetting.




	2. Purple Magic

**Summary for the Chapter:**

> Anything related to purple magic and the Perseverance Soul

Note: I will be referring to the Perseverance Soul as "Purple" for the duration of this chapter.

  * Purple’s weapon, the Torn Notebook, grants invincibility frames but deals less damage than even the toy knife. I like the idea that the low damage is due to how it’s being used. I headcanon that Purple was an actual wizard, or at least was learning how to be one, and he/she used the notebook as a makeshift spellbook, with all kinds of basic attack spells (attack) and notes on how purple magic works (invincibility frames). But Frisk doesn’t know how to do any of that, so they just hit people with it.



  * KR (Karmic Retribution) is also purple, so that may have been the type of damage spell that Purple learned how to use. 
    * What if the Karma page is the page that got torn out, and Sans found it?



  * Second side note: With the “web” movement style and with Karma being a poison sort of attack (that happens to be flavored as “you feel your sins _crawling on your back_ ”), I’m guessing that Purple really liked spiders.



  * More about Inv. Frames, from a Tumblr post I found once (Sorry I don't remember whose blog it was from, someone sent it in anonymously anyways): "The way I see it, magic is an extension of the user's soul. If you consider each soul to have an unique wavelength, then one magic attack is essentially passing that wavelength through the opponent. As a result, the opponent's soul temporarily matches that wavelength, leading to them being temporarily invincible to any attacks."



  * OK, ordinarily, I wouldn't have added someone else's headcanon, but you need to see that to understand what I'm going to add onto it. If the wavelength thing is true, then the extended Inv frames mean that Purple figured out a way to make you stay “in tune” with other monsters longer. 
    * And you have no inv. Frames during the Sans fight because you’re never on the same wavelength as him. You're too stubbornly different from him and he can never understand you.
    * Also, please note that **the glasses have a lower DEF than the tutu,** because maybe it means you have to lower your defenses to be on the same wavelength with someone, which seems like a very Undertale thing to say.




	3. In-universe Explanations

**Summary for the Chapter:**

> In-universe explanations for why certain game mechanics exist.

  * **“Check”** is a magical ability all monsters know. It’s a quick and easy way to get to know someone. Chara learned it from the Dreemurrs.



  * Looking at someone’s HP or LV is considered rude, and those are also more well-guarded knowledge than ATK and DEF. The only monsters who know what your LV actually is, are Sans at the Judgement Hall (but he's only that invasive because he wants to confirm whether or not you're a threat to the universe) and Undyne (proven because she knows if you killed someone, even if it was back in the Ruins) (she checks because she's just generally suspicious of humans and doesn't care about being rude).



  * **Save points:** At a save point, you’re saving the locations and states of all monsters and objects at that particular time. (Seems like I’m just stating the obvious right now but bear with me.) To save the locations of the monsters, the save point would need to locate them first. So, when you save, you’re reaching out and feeling the magic of the monsters in the area. The hope of their magic restores your HP bar. (Or, for an evil protagonist, seeing how few left there are gives you hope and restores your HP bar.) 
    * Also, that’s how the evil protagonist can sense how many monsters are left in an area.



  * **Golden Flowers** are a magical plant unique to the area around Mt. Ebott. They evolved from some other kind of plant after being exposed to the magic of the barrier for thousands of years. Their most notable property is their ability to negate fall damage. This is why Frisk still has full health right after they fell.



  * Monsters’ magic is constantly emitted from them in expression bullets and musical auras (also called “theme songs”). Temmie’s cat ears are used like normal ears, while her dog ears can hear theme music. I thought of this because the Temmies in the village sing their own theme song.



  * **Magic and dodging** : Monsters _could_ learn how to dodge, but because their bodies are attached to their souls, it’s much harder for them to dodge bullets than it is for humans because they’d have to dodge them physically. That’s why most of them stick to blocking bullets with their own magic. But, using magic to block only works on magic attacks, not physical attacks. So, when the human attacks them, they try to block and it fails. 
    * Sans knowing how to dodge means that he has either trained in case of meeting a human or has fought humans before. Or he’s a Darkener. But that’s another can of worms, that I'm not ready to open.



  * **Shop Tem** can’t count high enough to realize she already has 1000G, so she needs it handed to her all at the same time.



  * If you ACT, Monsters drop coins after a battle out of politeness, as an apology for dealing damage or as a thank-you for helping them. If you fight, it’s just because they’re scared.



  * The reason you encounter more monsters when you walk around in circles or do the Frisk Dance is because they come over to see what the heck you’re doing. Seriously, you look ridiculous doing that.



  * So, you know how Gerson knows you can’t fight him in the shop menu? That’s because there’s actually a spell that keeps you from fighting in shops. It was invented super long ago, to protect the shopkeepers who only wanted to help travelers. The shop must have at least 3 walls, a shopkeeper, 4 items to sell, and information for friendly travelers. If these qualifications are met, the monster can activate the spell, which prevents anyone in the building from attacking.



Gerson knows about this spell and was there when it was cast on his shop. He was probably even there when it was invented. Not likely that he would remember how to cast it, though.

The Snowdin Bunny shopkeeper knows about the spell but isn’t sure if it’s real or just superstition. She makes sure to keep her shop in good condition and always be polite to travelers just in case.

IDK what’s up with the Temmies, but it’s plausible that they were super powerful spellcasters in the past and knew ALL about the shop spell, but the current Temmies don’t know about it. I mean they do have a rich history. We just have no idea what it is.

The spell in MTT resort was set up back when it was just an apartment building. People forgot about it when it closed. Mettaton didn’t even know that room had been a shop previously when he set up his fast-food room in there. And he especially doesn’t realize that Burgerpants talking to the customers reactivated it, and that if there was ever an evil-human-related catastrophe, Burgerpants would be one of the only people in the building to survive and would maybe be able to keep other NPCs safe. I bet if he knew this, he wouldn’t be so against Burgerpants talking to the customers.

Bratty and Catty cast the safety spell by complete accident when they were trying to arrange their garbage shop for an ~~Instagram~~ Undernet picture. It’s a really unlikely coincidence, but in a universe like this one, why not?

Nice Cream Guy doesn’t qualify, since his shop is mobile and doesn’t have walls, and also because he only sells Nice Cream.

Grillby probably would qualify, except that he doesn’t like to talk.


	4. Let's Talk About Spiders

**Summary for the Chapter:**

> This is my set of headcanons about spider monsters like Muffet. Feel free to skip this if you think it'll be too creepy. It probably won't (I don't write creepy things), but IDK your tastes.

  * Some people have called out Muffet for being a cannibal. But she isn't. She doesn't use sentient spider-monsters in her cider and donuts, only the normal, nonmagical spiders. The proof? The cider says "made with whole spiders." This wouldn't be possible if she was using spider-monsters, because they would just turn to dust. Thus, she has to be using the regular, nonmagical and nonsentient kind.



  * But how do you tell the difference? What about the spiders that carry the signs and telegrams? They look like small, regular little spiders, but they have to be monsters, right? Not necessarily. I think that Muffet and other spider-monsters like her have a certain degree of control over nonmagical spiders. Like, say, a spider-monster would be the one in the Ruins actually writing the telegram, but they could make the small spiders collect gold and sell donuts for them.



  * Spider Clans/Colonies have been overlooked by the Dreemurr dynasty for help for a long time, but it’s not because the Dreemurrs hate spiders or anything. It’s just that they’re powerful, fire-wielding boss monsters, so spiders are naturally scared of them and generally try to stay away. Because of this, the Dreemurrs notice them less.



  * Spiders are naturally afraid of any fire monsters, actually. You know how loads of people ship Muffet and Grillby? Yeah, I doubt that would work out. If anything, I bet Muffet is terrified of Grillby.



**Notes for the Chapter:**

> Sorry for the short chapter! These are separated by sections, not by length, so it makes sense for some of them to be a lot longer than others, though.


	5. Environment/Setting

**Summary for the Chapter:**

> This is all about the Underground, and how it affects monsters, and how their magic affects it.

  * **Golden Flowers** are a magical plant unique to the area around Mt. Ebott. They evolved from some other kind of plant after being exposed to the magic of the barrier for thousands of years. Their most notable property is their ability to negate fall damage. 
    * They can grow in even dark conditions (as proven by the patch in the dump) and, considering that they’re cultivated deliberately by Toriel and Asgore, whereas they grew on their own in the swampy dump, probably prefer moist or swampy ground.
    * Meaning that, in the overworld, they probably grew in a swampy area or on the banks of a lake or river near the mountain.
    * It’s unclear if golden flowers have red thorns naturally, or if Flowey can just summon those occasionally as part of “plant magic”.



  * **Trees in the Underground** are almost exclusively conifers, like pine and spruce. Thematically, this makes sense for Snowdin, which is the “ice level” of the game and is Christmas-themed. But, in-universe, it also makes sense. Conifers often grow on high elevations because they can handle the snowy-town weather up there. So, it would make sense that if any seeds fell down into the hole that these seeds would grow into conifer trees. 
    * Conifers don’t just appear in Snowdin, either. You can see some pine-tree-looking things with glowing trunks in parts of waterfall, seemingly adapted to the particular magic of that area.



  * **_Plants don’t talk, dummy!_** By the time Frisk arrives, there are very few plant monsters left. There’s Vegetoid, a relatively weak monster living in the Ruins (probably to be closer to the sunlight) and that pirhana-plant-looking guy in Grillby’s (probs doesn’t need as much sun because it’s similar to carnivorous plants, but still needs heat and basically lives in Grillby’s). I feel like there were probably a lot more plant monsters and monsters with plant-based powers before they got trapped, but due to a lack of a plant-friendly environment, they went extinct or adapted and changed into other kinds of monsters. IDK, I just really like the idea of Flowey not being the first creature to be able to control vines.



  * Just as plant/sunlight/star monsters became less common underground, rock elemental/ crystal elemental monsters became more common. (Ice Cap, for example, is a Crystalline Water Elemental. On the surface, there would probably have been more straight-up water elementals. And Vulkin is a Rock/Fire Elemental, which could really only develop in volcanic conditions.)



  * **The overworld** probably used to have magic as a commonplace thing, although not to the degree that it is in the Underground. This was slowly lost as the monsters were all locked away in one location.



  * **The Ebott Cave System** is crazy-full of magic. It started out as this huge, but plain, cave system, with Ruins being sort of autumnal / room-temperature, Snowdin being a cold cave, far from surface light, Waterfall being full of underground lakes, fungi and crystals, and Hotland being closer to the earth’s core/ the base of the volcano, before the cave system starts heading upwards again with New Home. Since Snowdin was cold, furry monsters and cold elementals tended to like living there. The cold-elemental magic intensified in the condensed area and turned the area into an isolated winter wonderland. Same sort of thing happened with glowy and aquatic monsters in Waterfall, and fire monsters in Hotland;


  * **Rainforest** There could probably be a rainforest somewhere off to the side between Waterfall and Hotland. It would have hot, muggy/steamy conditions. Probably a lot of the tough bug/frog monsters from the core would live there. However, it would be nowhere near as diverse as the overworld rainforests, having only bell blossoms/ bridge seeds, echo flowers, pine trees, and possibly golden flowers. 
    * The rainforest could also have Swinging Vines, as those are a popular video game mechanic.




End file.
